The long-term objective of this proposal is a more complete understanding, at the molecular level, of the regulation of hemoglobin synthesis and the role of erythropoietin in this regulation. One aspect of the mechanism of erythropoietin action on red cell differentiation is that of initiation and control of transcription of the globin genes. The transformed mouse cell lines, IW32 and NNlO, which secrete erythropoietin constitutively, are good models in which to study this process since they can also be induced, by hemin or butyrate, to transcribe the alpha and beta globin loci. A control cell line (201), which does not secrete erythropoietin, transcribes the alpha globin message but not the beta after exposure to hemin or butyrate. The problem thus is one of the mechanism of differential gene expression and the possible role of trans-acting, inhibitory factors in the regulation of the beta globin gene. This model may be related to various human disorders in which either a globin gene is not expressed or one is expressed and should be suppressed to permit the expression of an alternative. IW32 cells have a rearranged and amplified erythropoietin gene and are being used to study the structural features that permit constitutive expression of the erythropoietin gene.